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在大地电磁实测数据中阻抗张量次对角元素的相位值超出正常象限(一、三或二、四象限)的现象称为相位超象限.这种现象无法利用各向同性介质的一、二维反演来解释,而与特定形态的三维各向同性介质有关的电流槽效应有可能是引起相位超象限现象的原因之一.本文首先重建了四个能引起相位超象限的三维各向同性介质理论模型,对模型结构和响应特征进行了总结.随后结合麦克斯韦方程组介绍了电流槽效应产生的原理,并通过近似解析公式分析了电流槽效应对电、磁场的影响.最后,我们针对最近几年来在青藏高原北缘观测到的相位超象限大地电磁测深数据,重点对河西走廊北侧的三个连续相位异常数据进行了三维反演研究,反演模型能够很好地拟合实测的相位超象限数据.通过对模型中存在于上地壳的不同规模高导异常结构进行三维正演检验,最终确定位于测点北东方向的巴丹吉林沙漠构成了区域高导体,它与紧邻测点东侧的局部高导体相连,在平面上形成了“L”型的高导构造,是引起河西走廊北侧相位超象限大地电磁观测数据的主要原因.除此之外,紧邻测点西侧的孤立高导体也会对相位异常的分布范围产生影响.
The phenomenon that the phase value of the sub-diagonal elements of the impedance tensor beyond the normal quadrant (one, three or two, four quadrants) in the magnetotelluric measured data is called the phase super quadrant. This phenomenon can not make use of the one- Dimension inversion, and the current slot effect related to the three-dimensional isotropic medium with specific morphology may be one of the reasons that cause the phenomenon of phase super quadrants.In this paper, we first reconstruct four three-dimensional isotropic Medium theory model of the model structure and response characteristics were summarized.Then combined with Maxwell’s equations introduced the current slot effect of the principle and the approximate analytical formula analysis of the current slot effect on the electrical and magnetic fields.Finally, Over the past few years in the northern margin of the Qinghai-Tibet Plateau observed telemetric electromagnetic ephemeris data focus on the north of Hexi Corridor three consecutive three-phase inversion of anomaly data were studied, the inversion model can be well fitted to the measured Phase over quadrant data.Through the three-dimensional forward analysis of high-anomalous structures of different sizes existing in the upper crust in the model, the final position The Badang Jaran Desert in the northeast of the measuring point constitutes a regional high-conductor, which is connected to a local high-conductor near the east of the measuring point and forms a “L” -type high-conductivity structure in the plane, which causes the Hexi Corridor North In addition, the isolated high conductors in the immediate vicinity of the measuring point also influence the distribution of phase anomalies.